The long term objective of our research is to better understand the mechanisms underlying both normal and abnormal vestibular function. The focus of this proposal is to develop and refine methodology for detection of lesions of the semicircular canals and of the otoliths. The research strategy is to make quantitative measurements of vestibulo-ocular and vestibulo-spinal function in humans using paradigms suggested by the results of neuro- physiological studies and mathematical models of vestibular function. We will study normal human subjects and compare their response to those of patients with known vestibular lesions. The first project aims to detect lesions of the vertical semicircular canals. We will detect unilateral lesions through caloric irrigation with the head pitched to make the lateral canals horizontal. We will measure the vestibulo-ocular response to the caloric irrigation using the scleral eye coil and the vestibulo- spinal response using posturography. We will detect bilateral lesions and/or central lesions through measurement of the entire vector of the VOR, that is, horizontal, vertical and torsional eye movement, as elicited by rotational stimuli that excite the vertical canals. Our second project aims to refine methods of detecting lesions of the lateral canals. To detect unilateral lesions we will quantify head-shaking nystagmus in patients with peripheral or central vestibular lesions. We will also investigate a new form of head- shaking that excites the vertical canals, circular head shaking. Our third project aims to detect lesions of the otoliths. We will investigate the effects of eccentric rotation with one ear lateral to the axis of rotation to selectively stimulate a single otolith organ. We will use eccentric rotation with both ears anterior to the axis of rotation to stimulate both otoliths. We will measure the modulation gain and time constant of the VOR. Our results will provide new information useful in the assessment of patients with nystagmus, visual blurring and oscillopsia, vertigo dizziness, and disequilibrium.